C++ 由于链接中缺少虚拟函数，无法解析外部

主窗口中出现奇怪的链接错误。我还在主窗口中包含了这些类的头文件。但它仍然无法连接虚拟功能

我主要使用以下代码：

S3W::IFields *recordsTx = pConnection->GetTransmittedFields();
    FieldsDataList *derived = dynamic_cast<FieldsDataList*>(recordsTx);

    for (int j = 0; j < 2; j++)
    {
        VarField& record = derived->CreateDataItem();
        FieldsDataList *fields = record.getChildrenDataList();


        VarField& fieldGeom1 = fields->CreateDataItem();
        fieldGeom1.SetKey("geom");
        double x = 47;
        double y = 16;
        fieldGeom1 = VarField::fromGPS(new ImplGps(x, y));
}

以下是类的类定义：

//伪码

class VarField : public S3W::IField
{

 virtual S3W::IFields& getChildern() override;
    // Inherited via IField
 virtual FieldsDataList * getChildrenDataList() override;

}

我的领域是：

struct FieldsDataList;

namespace S3W
{
    struct IFields;

    struct IField : S3W::IListItem
    {
        enum class Type { NONE = 0, UINT = 1, DOUBLE = 2, STRING = 3 , GEOM = 4};
        virtual S3W::IGps* getGeom() = 0;
        virtual double getDouble() const = 0;
        virtual unsigned int getUint()   const = 0;
        virtual const char*  getString() const = 0;
        virtual const char*  getKey() const = 0;
        virtual Type getType() const = 0;
        virtual ~IField() { }
        IField() {} 
        virtual  IFields& getChildern()= 0; 
        virtual FieldsDataList* getChildrenDataList() = 0;
    };

---

我只看到这两个函数的声明，它们的定义在哪里？

struct FieldsDataList;

namespace S3W
{
    struct IFields;

    struct IField : S3W::IListItem
    {
        enum class Type { NONE = 0, UINT = 1, DOUBLE = 2, STRING = 3 , GEOM = 4};
        virtual S3W::IGps* getGeom() = 0;
        virtual double getDouble() const = 0;
        virtual unsigned int getUint()   const = 0;
        virtual const char*  getString() const = 0;
        virtual const char*  getKey() const = 0;
        virtual Type getType() const = 0;
        virtual ~IField() { }
        IField() {} 
        virtual  IFields& getChildern()= 0; 
        virtual FieldsDataList* getChildrenDataList() = 0;
    };